*GASP* LOOK AT HIM!! MY BABYYYYYYY AHHHHHHHHHHHH (i'm okay i promise lol-)
Hello! Ah, he really was so tiny back then. Seeing him compared to the present version really puts it into perspective 😌
For young Nightmare, the whole situation would have been incredibly confusing. One moment he was sitting beneath the tree, and with what felt like a single blink, he suddenly found himself in a completely unfamiliar place with a group of strangers staring down at him. Thankfully, they don't seem hostile, but between Killer's outburst and everything that followed, it would still be a lot for anyone to take in.
More than any of that, though, what would affect him the most is the fact that he isn't beneath the tree anymore, and Dream isn't with him. Young Nightmare's purpose was to protect the apples, and for that, both the tree and Dream were essential.
Even so, I don't think Nightmare would openly show much confusion. Despite his age, he was still a spirit, and in some ways, his way of thinking was actually much closer to his original nature than that of the adult Nightmare.
He would understand that something strange had happened to him, and he would also realize fairly quickly that there is nothing he can personally do to resolve the situation. So Nightmare would simply decide to accept it and wait to see how things unfold. Because of that, he'd be very well-behaved. He might occasionally stare at the gang with an expression that's impossible to read, but he wouldn't be particularly wary of them.
At first glance, he'd seem like a very innocent and kind child, and to be fair, he genuinely is. However, there is also something strangely detached and inhuman about the way he thinks, which is probably why he'd remain surprisingly calm throughout the whole ordeal. Besides, unlike Dream, Nightmare was never really the type to cause problems himself. He doesn't particularly enjoy interacting with mortals, either.
I imagine the atmosphere would start becoming much less pleasant if the situation dragged on for too long, but for now, it's honestly pretty adorable. After all, he'd technically become the smallest member of the gang. You could say Dust unexpectedly benefits from that particular situation 😆
Thank you for the ask! I hope you have a wonderful day 💕